вс, 7 окт. 2018 г. в 16:42, Karl Ove Hufthammer <karl@xxxxxxxxxx>:
Alexander E. Patrakov skreiv 07.10.2018 09:44:
>
> I don’t understand why this is happening. Shouldn’t
> ‘remixing-use-all-sink-channels = no’ just affect *upmixing* of
> sound,
> and leave 5.1 material alone?
>
>
> This is a known bug that appears because there are two 5.1 standards:
> proper 5.1 and 5.1 Side. The video player (I guess you use mpv) says:
> the extra two channels have to come from the side.
Looks like you’re right. If I run ‘ffprobe’ on my 5.1 test file, it returns:
Stream #0:1[0x1100]: Audio: dts (DTS-HD MA) ([134][0][0][0] /
0x0086), 48000 Hz, 5.1(side), s32p (24 bit)
So the video file (and mpv) seems to use the ‘5.1(side)’ standard.
(Which is a bit strange, since this is supposed to be a video file to
test a normal 5.1 setup, AFAICS.)
(speaking with my "DTS encoder author" hat on)
The issue is that it is a DTS file. DTS uses completely different channel names than what's found in PulseAudio source. The proper normative reference is:
page 19, table 5.4 (note that the presence of the LFE channel is transmitted separately).
Your file uses AMODE=0b001001=9, so the list of channels is: "Center", "Left", "Right", "Surround Left", "Surround Right". And there is also a 64x downsampled LFE channel. FFMmpeg-based decoders map "Surround" to "Side" because "Rear" also exists in other channel layouts and means something different. There is no way in DTS to express a layout with "Rear" but no "Surround" channels.
> But your system does not have speakers there, it has them on the rear.
> So PulseAudio attempts to remix. In fact, sound both with and without
> remixing-use-all-sink-channels is wrong.
What’s wrong about the remixing when one uses
‘remixing-use-all-sink-channels = yes’?
The rear channels will get not a copy of the side, but an average of front and side.
Alexander E. Patrakov
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